1. Field of the Invention
This invention relates generally to a system and method for allowing a vehicle engine to more quickly obtain its operating temperature at vehicle start-up and, more particularly, to a system and method for allowing a fuel cell engine for a vehicle to more quickly obtain its operating temperature at vehicle start-up by operating a fan in a reverse direction to limit the airflow into the engine compartment.
2. Discussion of the Related Art
Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. A hydrogen fuel cell is an electro-chemical device that includes an anode side and a cathode side with an electrolyte therebetween. For automotive applications, a series of fuel cells are combined in a fuel cell stack to generate the desired output power. The fuel cell stack includes a system of flow channels for directing the hydrogen input gas to the anode side of each fuel cell and air to the cathode side of each fuel cell. Further, flow channels are provided for a cooling fluid that flows through the fuel cell stack to maintain a thermal equilibrium.
It is necessary that a fuel cell operate at an optimum relative humidity and temperature to provide efficient stack operation and durability. A typical stack operating temperature for automotive applications is between 60°–80° C. The stack temperature provides the relative humidity within the fuel cells in the stack for a particular stack pressure. Excessive stack temperatures above the optimum temperature may damage fuel cell components, reducing the lifetime of the fuel cells. Also, stack temperatures below the optimum temperature reduces the stack performance. Therefore, fuel cell systems employ thermal sub-systems that control the temperature within the fuel cell stack.
A typical thermal sub-system for an automotive fuel cell stack includes a radiator, a fan and a pump. The pump pumps the cooling fluid through the cooling channels within the fuel cell stack where the cooling fluid collects the stack waste heat. The cooling fluid is directed from the stack to the radiator where it is cooled by ambient air either forced through the radiator from movement of the vehicle or by operation of the fan. Because of the high demand of radiator airflow in order to reject a large amount of waste heat on a relatively low temperature level, the fan is usually powerful and the radiator is relatively large.
At vehicle start-up, the fuel cell stack is typically well below its optimum operating temperature, especially in low temperature environments. It is desirable to raise the temperature of the fuel cell stack to its operating temperature as quickly as possible to increase the stack durability, which could take several minutes. However, the fuel cell stack is still able to produce output power that may be significant enough to operate the vehicle. If the vehicle operator does operate the vehicle prior to the fuel cell stack reaching its optimum temperature, ambient air is undesirably forced through the radiator into the engine compartment from the motion of the vehicle, which acts to convectively cool the fuel cell engine. This convective cooling increases the time that the fuel cell stack will reach its operating temperature, thus affecting the stack durability and lifetime.
Various techniques have been proposed in the art for reducing the airflow to the engine compartment of a vehicle so that the engine will more quickly reach and maintain its optimum operating temperature. In one known technique for an internal combustion engine, the vehicle operator was required to attach a plastic cover to the front grill of the vehicle in a low temperature environment to reduce the airflow to the engine. Such a solution in today's market would not be acceptable. It is further known to employ louvered panels adjacent to the front grill of the vehicle, where the panels are opened or closed automatically depending on the external temperature and the operating condition of the vehicle. However, the louvered panels have several disadvantages, including high cost, additional weight, additional packaging space, and icing that may prevent the panels from opening in winter conditions.
It is further known in the art to operate a fuel cell stack or a combustion engine inefficiently during vehicle start-up to increase the waste heat produced by the stack or the combustion engine. However, this solution had the disadvantage that it increases fuel consumption. It is also possible to provide thermal insulation around the fuel cell engine to decrease the convective cooling. However, this solution required packaging space, additional cost and reduced thermal losses at hot ambient temperatures and high system loads when heat dissipation is necessary to reduce the thermal load of the radiator.